promisekit-fetch.swift

func fetch(url: URL) -> Promise<Data> {
    return Promise { seal in
        URLSession.shared.dataTask(with: url!) { data, _, error in
            seal.resolve(data, error)
        }.resume()
    }
}

fetch(url: <backendURL>).then { data in
    return JSONParsePromise(data) // we skip the wrapping of JSONParsing
}.then { imageurl in
    return fetch(url: imageurl)
}.then { data in
    imageView.image = UIImage(data: data)
}.catch { error in
    // in case we have an error
}